Think about it: turntables are electro/mechanical devices that transform LPs' grooves into sound. OK, that's not exactly right, it's the phono cartridge's job, but the turntable provides the platform to make that happen.
Phono cartridges are incredibly sensitive transducers, so they don't just convert the grooves undulations into sound, cartridges can also pick up bad vibes from footsteps, dancing, etc, and even the rumble of the turntable's motor. Those background noises muddy the sound.
The turntable's placement can negatively affect its sound quality. Wobbly furniture is a huge no-no; put the turntable on a solid shelf or stand. If you can move the cabinet, even a little with a push of your finger, try this: tightly wedge a few paperback books between the back of the furniture and the wall. The goal here is to eliminate any possible lateral movement. Wobble elimination can improve the turntable's sound; bass will be deeper, better defined and overall clarity will be enhanced.
Next, if you have a bubble level, use it to make sure the turntable platter is perfectly level (side-to-side, and front-to-back). If your turntable doesn't have adjustable feet, try placing coins under the feet to level the turntable.
If you have a belt-drive turntable and know how to remove the belt, take it off. Wash it with warm water to clean off debris that's accumulated over the years. Then put it back on. Might make a small difference.
The quality of your phono cartridge is not only very audible; an old or worn stylus (needle) can permanently damage record grooves. When in doubt, buy a new cartridge. I like Audio Technica's AT-95 ($50) and Grado's Prestige Black ($60). These two are standard-mount cartridges, and they will work on many turntables, but some 'tables require "P Mount" cartridges. If you're not sure, read the manual or check with the turntable manufacturer.
Clean records sound better than dirty or dusty ones; a gentle wash with warm water and a little dish detergent can dramatically improve the sound. After washing and lots of rinsing, shake as much water off the LP as you can, and then stand it on paper towels, leaning against the wall to dry.
What you plug your turntable's cables into--a receiver or integrated amplifier--can play a large part in the sound you hear. Budget models are likely to be marginal performers and prone to hum or add noise. A workaround solution is to use a quality phono preamplifier, such as Audio Technica's AT-PEQ3, which sells for $60 on Amazon. The phono preamp is hooked up between the turntable and the receiver or amp. You can then plug the phono preamp into an unused "Aux" or "Video" audio input on the receiver or amp.
The vinyl boom shows no signs of slowing down, and judging the by the ever-increasing selection of LPs on the market this is a great time to make the plunge and buy a turntable. New titles are coming out all the time: Tom Waits' "Glitter and Doom Live," Bob Dylan's "Christmas In The Heart," Lady Gaga's "The Fame," Animal Collective's "Fall Be Kind," and Norah Jones, The Fall" are all available on LP. Bargain hunters can find tons of cheap used vinyl at yard sales and record shops.
If you have any turntable setup tips or tweaks, please share them in the Comments section.